Acronyms used herein are listed below following the detailed description. Dual connectivity is known in the wireless arts; for example a cellular base station and a WiFi access point may cooperate when providing wireless service to a UE where the cellular base station utilizes a cellular RAT for its portion of the dual connectivity and the WiFi access point utilizes an IEEE 802.xx RAT for its portion of the dual connectivity. Another example is the baseline dual connectivity described in 3GPP TS 36.300 which provides an aggregation of radio resources across two LTE eNBs. The 3GPP organization is developing a new radio access technology (NR for new radio, or sometimes referred to as 5G) that may eventually replace E-UTRAN (also known as LTE or 4G). The radio access nodes for NR are referred to a gNBs, and it is anticipated that early deployments of gNBs will not be within a standalone 5G system but will operate by sharing some of the existing LTE infrastructure such as core network operations and gateway servicing.
To bridge the gap in time until the NR infrastructure is more fully deployed, it is desirable to provide dual connectivity to UEs where the LTE radio access node eNB will be communicating with the UE using the LTE RAT and the gNB will be communicating with the UE using the NR RAT. One key principle adopted in standardizing this EUTRAN-NR Dual Connectivity (EN-DC) is that the LTE and NR nodes should act as independently as possible, meaning each node can provide and manage its own radio resources in EN-DC operation without having to comprehend what the other node is doing. An example of comprehension/understanding relates to the aspect of having one node to interpret either the other node UE radio capabilities or the radio resource configuration provided by the other node. One purpose of this is to retain separation so the development of NR can evolve independently of LTE such that the LTE node does not need to be upgraded upon every NR upgrade; another important purpose is to allow easy interoperability between nodes made by different vendors/manufacturers by ensuring each node is as independent as possible.
In this regard the different radio access nodes need to have some degree of coordination regarding the UE capabilities to ensure both nodes respect the overall UE configuration limitations so that the total UE capabilities are neither individually nor jointly exceeded, some of which may be at least partially dependent on what is configured for the other radio access system. 3GPP document R2-1706859 by Nokia, Alcatel-Lucent and Shanghai Bell [3GPP TSG-RAN WG2 NR Adhoc #2; UE capability structure and coordination aspects for MR-DC; Qingdao, China; 27-29 Jun. 2017] broadly categorizes UE capabilities into sub-groups: radiofrequency (RF) capabilities (band combinations and capabilities that are per band combination); physical (PHY) capabilities (receiver, MIMO and TM capabilities, feedback, codebooks etc.); protocol-specific capabilities (MAC/RLC/PDCP based capabilities), measurement specific capabilities; feature specific capabilities; UE category indication; and inter-RAT capabilities (e.g. frequency bands supported by inter-RAT). How to implement this capability coordination has not yet been resolved in 3GPP. The quandary is that if each node would completely understand its own limitations it would not need to understand the other node's limitations, and could therefore do independent configuration. But for the case of inter-RAT DC there will still need to be some coordination in at least some cases so each node has to at least comprehend which capabilities would require some coordination. It is not desirable to adopt the LTE dual connectivity-based solution (such as the LTE-DC and LTE-WiFi example above) where the capabilities and configuration of each node are fully comprehended by the other, for this would undermine the independence of the NR system from the LTE system.
Document R2-1706859 referenced above provides one approach that supports that can be summarized as an ‘index-based’ capability coordination that might preserve this inter-RAT independence. 3GPP document R2-1704129 by Qualcomm [3GPP TSG-RAN WG2 Meeting #97bis; LTE/NR capabilities dependencies; Spokane, USA; 3-7 Apr. 2017] describe a similar approach.
Embodiments of these teachings aim to ensure that, in the context of inter-RAT dual connectivity, the capability coordination between LTE and NR minimizes the need for comprehension of the other RAT capability and configuration details.